In recent years, various kinds of digital equipment such as digital cameras, digital camcorders, and cellular phones are becoming lighter and more compact, which requires a semiconductor package that may be mounted with a higher density.
Now, as a mode which enables mounting with a high density, a stacked semiconductor device receives attention. A stacked semiconductor device is formed by further connecting a semiconductor package in which a semiconductor element is mounted on a wiring substrate to another semiconductor package. By three-dimensionally disposing semiconductor packages, the footprint may be reduced, which enables mounting with a high density.
However, in a stacked semiconductor device, semiconductor elements which are heat sources are three-dimensionally disposed. Therefore, heat dissipation from the semiconductor elements is not sufficient, and there is a possibility of malfunction and connection defect at a connection terminal due to temperature rise of the semiconductor elements. More specifically, in the case of an ordinary semiconductor package, much of the heat from a semiconductor element is released via a connection terminal to a motherboard. On the other hand, in the case of a stacked semiconductor device, heat from a semiconductor element mounted on a semiconductor package which itself is not directly mounted on a motherboard cannot be sufficiently released to the motherboard.
In order to solve such a problem, U.S. Pat. No. 6,188,127 proposes a method in which, in a stacked semiconductor device, a heat dissipating member is attached to each individual semiconductor package to dissipate heat into the air.
The method described in U.S. Pat. No. 6,188,127 dissipates, via the heat dissipating member, heat into the air, the heat being generated from a semiconductor element mounted on a semiconductor package which itself is not directly mounted on a motherboard. However, the thermal conductivity of air is as low as 0.02 W/mK, and thus, it is hard to say that such heat dissipation into the air is effective.
The amount of heat generated from the semiconductor element becomes larger as the functionality of the semiconductor element increases. Further, the efficiency of heat dissipation decreases as the connection terminal is miniaturized and the number of pins increases for the purpose of mounting with a high density. Therefore, when the amount of generated heat is large, measures including increasing the size of the heat dissipating member are required to be taken. However, there is a limit to the size of the heat dissipating member, and increasing the size thereof to an extreme is impossible in reality.